The so-called "DNA methylation" (methylation) is the addition of methyl groups (-CH3) to DNA molecules without affecting the DNA sequence, thus changing the expression of genes. DNA methylation is an important link in controlling the genetic expression of genes. Its location will have a greater or lesser impact on disease, development, and cell differentiation. The external stimuli and lifestyle received by the organism will also cause differences. DNA methylation, thereby affecting subsequent gene expression.

Methylation marks from the parents' DNA are erased when a fertilized egg is first formed, then re-established as the individual develops. To a certain extent, DNA is like a person's initial design blueprint, and the environment, lifestyle or other stimulation factors experienced will make various small modifications to the blueprint, thus affecting the subsequent gene expression. . As epigenetics develops, detecting these tiny modifications, such as the occurrence of DNA methylation, has the opportunity to help us understand disease or certain physical conditions.